When drilling in earth formations, various waste materials including drilling cuttings (i.e., pieces of a formation dislodged by the cutting action of teeth on a drill bit) are produced. Often, in circumstances where surface storage and disposal resources are limited, these waste products may be re-injected into the formation through a cuttings re-injection (CRI) operation. While the term “cuttings re-injection” is used to describe the operation, it should be understood by one of ordinary skill in the art that the term is used generically to describe any process whereby drilling waste including, but not limited to, drill cuttings, produced sands, water, scale, and other byproducts, are reintroduced into the formation using methods and apparatus described herein.
Typically, a CRI operation involves the collection and transportation of cuttings from solid control equipment on a rig to a slurrification unit. The slurrification unit subsequently grinds the cuttings (as needed) into small particles in the presence of a fluid to create a slurry. The slurry is then transferred to a slurry holding tank for conditioning. The conditioning process affects the rheology of the slurry, yielding a “conditioned slurry.” The conditioned slurry is pumped into a disposal formation by creating fractures under high pressure. Typically, the conditioned slurry may be delivered to the disposal formation through a casing annulus or a tubular system to a dedicated disposal wellbore but, in circumstances where such a wellbore is unavailable, the slurry may be delivered to a disposal section of a producing wellbore. The conditioned slurry is often injected intermittently in batches into the disposal formation. The batch process may involve injecting roughly the same volumes of conditioned slurry and then waiting for a period of time (e.g., shut-in time) after each injection. Each batch injection may last from a few hours to several days or even longer, depending upon the batch volume and the injection rate.
The batch processing (i.e., injecting conditioned slurry into the disposal formation and then waiting for a period of time after the injection) allows the fractures to close and dissipate, to a certain extent, the build-up of pressure in the disposal formation. However, the pressure in the disposal formation typically increases due to the presence of the injected solids (i.e., the solids present in the drill cuttings slurry), thereby promoting new fracture creation during subsequent batch injections. The new fractures are typically not aligned with the azimuths of previous existing fractures.
Release of waste into the environment must be avoided and waste containment must be assured to satisfy stringent governmental regulations. Important containment factors considered during the course of the operations include the following: the location of the injected waste and the mechanisms for storage; the capacity of an injection wellbore or annulus; whether injection should continue in the current zone or in a different zone; whether another disposal wellbore should be drilled; the required operating parameters necessary for proper waste containment; and the operational slurry design parameters necessary for solids suspension during slurry transport.
As many of the rigs used to drill oil and/or gas wells currently enjoy much smaller footprints than oil and/or gas wells of the past, the desired footprint for CRI operations has been reduced as well. As the CRI operation space has decreased, the need has arisen for space allocated to various pieces of equipment and systems to also decrease. Further, the decrease in available space and time spent preparing the site for CRI has accentuated the need for decreasing the footprint and preparation time for monitoring, as well as other associated equipment.
At locations where petroleum products are being recovered, refined or processed, a number of flammable gases may be present, including mixtures of oxygen, methane, ethane, propane, hydrogen sulfide and others. Standardized classifications for various types of hazardous locations have been adopted and assigned by regulatory agencies according to the nature and type of hazard that is generally present or that may occasionally be present.
Because electrical components, by their nature, may generate heat and sparks sufficient to ignite a flammable gas or other flammable mixture under even normal operating conditions, such components must be carefully designed, selected and installed when used in an area that is classified as hazardous. More specifically, the components must exceed certain minimum standards as to such characteristics as power consumption, operating temperature, current and voltage requirements, and energy storage capabilities. These standards are also established by regulatory authorities and vary depending upon the particular hazardous environment.